I. Field
The present invention relates generally to communication, and more specifically to time synchronization in a communication system.
II. Background
A multiple-access communication system can support communication for multiple user terminals by sharing the available system resources (e.g., time, frequency, and/or transmit power). Each user terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the user terminals, and the reverse link (or uplink) refers to the communication link from the user terminals to the base stations.
On the reverse link, a base station may receive transmissions from multiple user terminals. The transmission from each user terminal travels via a different set of signal paths. The signal paths for different user terminals typically have different channel gains and propagation delays. Consequently, the transmissions from these user terminals may arrive at different times at the base station for the same transmission starting time. The transmissions may interfere with one another if they are not properly time aligned at the base station. This interference may adversely impact the base station's ability to recover the transmission from each user terminal and may degrade performance for all affected user terminals.
A time control loop may be used to adjust the timing of each user terminal so that its transmission arrives at the proper time at the base station. The design of the time control loop may be challenging due to various factors such as, for example, difficulty in obtaining an accurate measurement of the arrival time of a transmission. This difficulty may be due to the manner in which the transmission is sent, adverse channel conditions, and so on.
There is therefore a need in the art for techniques to accurately measure arrival time at a receiver and to properly adjust timing at a transmitter in a communication system.